Mind-Switch!
by Mika Nakane
Summary: After losing a game to their own doubles partners, Marui and Niou are forced to drink Yanagi's "vegetable" juice. However, it turns out that the juice exceeded Yanagi's predictions, and switched Marui and Niou's minds, so that Marui is in Niou's body, and Niou is in Marui's. A friendship develops between them as they realize what life is like from another point of view.
1. Chapter 1

**A/N Okay, I came up with this because I needed SOME inspiration to write another fanfic, and I happened to watch the Cardcaptor Sakura episode where Li and Kero switch. Hence, this fanfiction. I will continue this one for about 5 chapters, or at least until I get (or someone gives me) an amazing idea that can put my mind to work. C'mon people, I don't care if it's cheesy, angsty, or just plain stupid, I need an idea!**

**I don't own Prince of Tennis.**

Chapter 1

Yukimura smiled at the games going on. After all, it was amusing to see doubles pairs playing against their partners.

"Game, Yagyuu-senpai and Jackal-senpai. 5 games to 3!" Kirihara called out nervously, trying to ignore the two tennis players on the other side of the court who were glaring at him, having just lost another game.

"Really Marui, try to improve your teamwork. You won't always be playing with me." Jackal advised, giving Yagyuu a high five before heading back to his position at the baseline.

"I agree. Niou-kun, you need to be flexible to whoever your partner is, and not just me." Yagyuu added.

"I don't care! If I have to play with _him, _I'd rather play singles!" Marui objected, pointing at his smirking doubles partner. "Niou-kun, be serious. Marui is becoming annoyed." Yagyuu sighed, although not dropping his stoic expression.

Marui couldn't tell if he obliged, but hastily went to the net when he saw Niou toss the ball up to serve. A normal serve was returned with a laser, which Marui struggled to reach but ended up too late as the ball bounced and crashed against the fence before he noticed it. "Niou! That was yours!" Marui glared.

"It was, but you were already trying to return it. Besides, Yagyuu's playing for real so even if I had reached it, I wouldn't be able to return it." Niou stated. Marui gave an exasperated groan, and swallowed his gum in annoyance when their kouhai said "Jackal-senpai and Yagyuu-senpai win, 3 games to 6…"

Both doubles pairs walked up to the net to shake hands with their opponents. It was then that the misfortune started, if it hadn't already.

"Tarundoru! That was a terrible match!" Sanada glared. Yanagi placed a hand on his shoulder and calmly smiled at Yukimura. Yukimura, understanding, nodded in approval.

"While it may have been a poorly played match, I can assure you that after drinking this, your playing capabilities will increase exponentially. Imagine all the potential that could be yours." Yanagi started.

Kirihara blinked in confusion. So did most of the other regulars. Because, you know, they have to blink… Oh, nevermind.

"Meaning, Yukimura and I both advise Marui and Niou to drinking this juice made by my friend Sadaharu. It's full of nutrients, and with both guarantee it to be one of the best juices he has made so far." Yanagi finished, and held out two cups containing a bubbling, rainbow coloured liquid.

Marui gulped nervously. "Um, Buchou, you didn't actually say it was okay for us to drink this, right? I mean, it's… changing colours, and looks really toxic."

Yukimura gave the self-proclaimed tensai a smile. "I think it's perfectly safe. Besides, if it can enhance both of your playing abilities, it's great, right?", he reasoned. He waited while Yanagi handed Marui and Niou the cups. They stared at it for a while, before deciding to chance it. Besides, not _everything_ Inui made was utterly disgusting and poisonous, right? …Right?...

* * *

Judging by the speed that Marui and Niou ran to the washrooms, the regulars could correctly decide to never, _ever, _drink anything made by Yanagi's friend. Ever.

Marui and Niou ran to the washrooms at such a speed that they put the cross-country runners to shame. Unfortunately, by the time they got there, they had already swallowed most of the drink. Surprisingly, it was tasteless. But Marui _knew_ that Yanagi put things other than vegetables in the drink, if the vinegar and squishy things he tasted was anything to go by. So, when they reached the washroom, all they could really do was try to spit out anything left in their mouth and faint.

* * *

"Niou-senpai! Marui-senpai! Are you okay?"

Opening his eyes a little bit, he could see Kirihara looking at him with concerned eyes.

"No, I am certainly NOT okay, brat! I am going to freakin KILL Yanagi for making me drink that stuff, dammit!" he responded automatically. His eyebrows raised when their kouhai looked at him, hurt.

"Marui-senpai? Are you okay? Why did you call me a brat? I know the juice must have tasted bad, but I didn't think you would want to kill Yanagi-senpai…", Kirihara trailed off. Widening his eyes, he shot awake, surprised. Did Akaya just call him Marui? This was a joke, right?

"Huh? I didn't call you anything, Akaya! And I would never want to kill Yanagi! He's annoying, yes, but even I wouldn't go that far!" the voice behind him protested. Kirihara looked genuinely confused.

"But, Niou-senpai, you're always saying mean things about his potions! And, I was talking to Marui-senpai." Kirihara informed. "What do you mean, I _am _Marui." the voice continued.

"No you're not," Kirihara stated, "You're Niou-senpai."

"What do you mean, brat, I'm right over here." he snapped.

Kirihara stared, confused.

"Ok, what's going on?" he shouted, and raised himself from his sleeping position to see the other two who were also in the room. This action was probably the smartest for him, but the others might have preferred to take their own sweet time to notice.

Marui yelled. "There's two of me!" he said, pointing at the "Marui" who had just stood up. Niou looked just as confused. "No, there's two of _me._ You've got white hair."

"What? Could it be that… that Niou-senpai and Marui-senpai have switched bodies?" Kirihara asked curiously. Hey, he was only a kid. These things didn't happen often.

The two looked at the mirror.

The scream could be heard throughout the school and even reached the tennis courts and soccer fields.


	2. Chapter 2

**A/N READ THIS FIRST**

**Okay, keep in mind that from now on, I will refer to Marui as Niou, and Niou as Marui. But when someone who DOESN'T know they've switched is talking, they mean who they see. So, if Yagyuu says "Niou", he means NIOU, but doesn't know that Niou is actually Marui.**

**Another exception is when I use a full name. Niou Masaharu is NIOU, and Marui Bunta is MARUI.**

**Again, MARUI=NIOU, and NIOU=MARUI whenever it's not someone talking.**

Chapter 2

"So, Niou-senpai and Marui-senpai have switched minds? How?" Kirihara asked curiously.

"Must be that stupid juice that Yanagi gave me. I swear, when I get back to my own body I will prank him until he regrets ever living…" Marui grumbled. Sighing, Niou looked at the mirror in the washroom they were in. It was horrifying.

"Well, we better go back and tell Yukimura-buchou about this. I don't want to be you forever." Niou whined. Suddenly, Marui grabbed his wrist. Niou's head snapped back to look at him.

"Actually, me and Yagyuu do something like this pretty often. Except, we don't really change bodies. It's more like we act and dress as each other." Marui explained.

"Your point?"

"How about we do the same thing, except with you and I? It's even easier in a way! Now we don't have to worry about people finding out because I'm much taller than you." Marui continued. Niou gasped. "No," he objected, "I will never be you! And I don't want to be you! Sanada-fukubuchou always assigns you extra laps, meaning that I won't have time to eat sweets!"

"You can't eat sweets anyway. Besides, you're in my body now, and I rarely eat anything high in sugar. If I'm right then you'll even skip meals sometimes." Marui remarked. Niou stared in horror.

"Look, just do this for a week, okay? After that we can tell everyone that we've 'switched', and Yanagi can find us a potion to get us back to normal."

Niou looked hesitant.

"F-fine, but we'll be found out within the first day! I'm not good at acting!" he exclaimed.

"Aww, is our tensai scared that he can't even act?" Marui teased. Niou glared.

"Fine, I'll do it! And I'll be a better you than even you can be!" he declared.

* * *

Kirihara had returned to the tennis courts right after he was able to confirm his senpai-tachi were switched. His first thought was _I should tell everyone what happened! _But then he realized that Yanagi-senpai was giving him a strange look, and he got the feeling that he wasn't supposed to say anything.

But, he was incredibly confused when the two showed up a while later, acting exactly like who they looked. Niou-senpai was smirking, and Marui-senpai was chewing bubblegum.

"Are you two alright?", Yukimura asked in a concerned voice, "Did it taste that bad?"

The two nodded furiously, until Marui (Niou, remember) nudged his arm, signaling that Niou Masaharu doesn't nod furiously. Niou (Marui, remember), realizing, quickly switched to an annoyed glare, and Marui nodded in approval.

"Tarundoru! 30 laps for being late, both of you!" Sanada barked, and Marui and Niou rushed off to run around the court while the other regulars pondered on their actions.

"It is not in Niou-kun's behaviour to nod like that. He seemed to be acting oddly." Yagyuu told them. The others had similar thoughts.

"Perhaps it's just Niou being weird. Marui seemed normal. They'll be fine soon." Jackal replied, and urged the practices to continue so that he could face Yagyuu in a singles match.

Marui, while running, had heard this. "See, Bunta, I'm a much better actor than you are." he teased.

"Shut up! Just because you managed to fool Jackal, doesn't mean you got my personality correct! I don't just chew gum, I blow bubbles with it!" Niou shot back in an annoyed voice. Nodding, Marui shaped the gum over his tongue, and prepared to blow.

* * *

"You've got to be kidding me. I am NOT taking it this far!" Niou said stubbornly, his arms crossed over his chest. They were done changing, and as much as Niou hated it, Marui had forced him into wearing his uniform.

"I'm about a size larger than you," Marui had explained, "So your uniform won't fit you anymore. Yagyuu and I are the same size, so it's a different case then."

"Fine, I'm okay with the uniform. But now we have to go to each other's houses instead of our own! I don't want to spend a week living in your house! It's probably covered in traps and stuff!" he protested. Marui chuckled. "It's not _that _bad. Besides, I've had to eat more sweets in this past hour that I've eaten in a year. Only my sister will be home, and with any luck, she'll ignore you."

Niou's expression softened. So Niou Masaharu rarely saw his parents? If that was the case, then he'd be surprised when the Marui's ate dinner together everyday.

"…Fine. But the moment I see anything weird, I'm blaming you!" he confirmed with a glare.

Marui chuckled again and gave Niou the address of his house, with Niou doing the same afterwards.

* * *

Niou glared. This just wasn't his day!

On the way there, he had accidently missed a road and ended up having to walk twice the distance to make up for his mistake. Then he realized that he couldn't read a few streets on the map due to the fact that Marui had written it in a hurry. This made him stomp angrily on the ground, and then sigh.

Niou reached into his pocket to pull out the cell phone he usually kept in there. Of course, it was no surprise to find that it wasn't there. He was in a different body, after all.

Cursing his misfortune, Niou looked through his bag in a futile effort to find something he could communicate with. This day seemed to be getting even worse. Now he was stranded on some random road with no way to communicate and no telephones nearby. Well, he _could _always knock on some random door and ask to use their telephone…

So that's what he did. After a bit of thought, he ran up to the house on his left and rang the doorbell impatiently. He was surprised at what happened when the door opened.

"Oh, Masaharu, you're home. Why didn't you just use your key? I was in the middle of sleeping." a girl about 22 years old, complained.

"R-right, I forgot. Um….. sis, this is where I live, right?" Niou asked awkwardly. Hey, for all he knew, this girl who claimed to know him could be a childhood friend of something.

"Don't be silly, of course it is." the girl glared, "Now are you going to come in, or will we wait until all the cold air wafts in?"

Niou hurriedly rushed inside the house before he angered his "sister" anymore. His eyes widened at the sight.

It was a beautiful house. He didn't notice at first, but it was large on the outside as well. A large hallway welcomed them with warm colours, and each room was unique and elegant. However, when he hesitantly wandered up the stairs, he noticed that the rooms upstairs were more creative, with each of the rooms having a different colour theme.

_Great,_ Niou thought,_ which room is supposed to be mine? I'd look like an idiot if I asked…_

He decided to check every room, opening 5 doors before finally opening one that looked like something Niou Masaharu would sleep in. The walls were lined with shelves of books and tricks, and there was the occasional paper full of possible pranks stuck on the wall. Niou stared in wonder at the room the school's trickster lived in.

The bed was large and inviting, but it paled in contrast to the other parts of the room. The bookshelf was something that surprised Niou the most. Everyone knew that Niou Masaharu wasn't a complete idiot, but he would have never expected to find books on advanced math in his room.

What interested him more, however, was the shelf on the opposite side of the room. It had many hand-made books, and Niou couldn't help but pick one randomly off the shelf.

The title startled him. _"How to act like Niou Masaharu"_, it read. Like it was reading his mind.

Putting the book aside, Niou decided to explore the house another day. It was already 10 o'clock in the night, and the events of the day made him confused and worried. He changed quickly into what looked like pajamas, and turned off the lights before jumping into the bed.

**A/N Ok, that was confusing, right? Just remember that for the part of when Marui enters Niou's house, Niou=Marui. Again, full names mean who they say. **

**For some reason, Niou has always struck me as either a rich boy with family problems, or a poor boy with family problems. I kind of prefer the former, and no one knows how Niou's house looks like, so let's just say he's rich in this fanfic, okay?**

**I'll be updating again soon ^_^**


	3. Chapter 3

**A/N I'll be returning to Niou (Marui's) story next chapter, but this chapter is focused on Marui (Niou). It takes place right after the trickster and tensai leave the school.**

**Also, sorry for not updating sooner! These two weeks have been hectic for some reason, so I couldn't find the time even though I had already typed up this chapter weeks ago and only needed to upload it...**

**Disclaimer: I don't own TeniPuri, and never will**

Chapter 3

Niou may have been in a hurry, but he took time to write the map neatly. Each road name was legible, unlike Marui's incoherent scribbles. Therefore, Marui was able to get to Marui Bunta's house in under 10 minutes.

It was a normal house, Marui learned. There was a car at the drive way, and the lawn was nicely kept with a few weeds here and there. Slightly nervous, Marui rung the doorbell. After all, Niou didn't mention anything of having a house key, and it looked like his parents were home.

The door was opened by a middle-aged man holding a mug of coffee, and wearing pajamas. "Oh, you're finally home," he welcomed, "We have a surprise for you!".

Marui entered the house curiously, wondering what the Marui's had prepared for him. When he was lead to the dining table, he faked happiness as a huge strawberry cake greeted him. The real Marui would have been delighted, after all.

Uneasily, Marui began to consume the cake, to find out that it tasted better than he thought. Niou Masaharu didn't have a sweet tooth, and therefore rarely ate sweets. But now he was in Marui's body, and the tensai absolutely loved the pastry. Somehow, Marui felt stronger after eating, and Niou Masaharu decided to start believing the red-head when he said that sugar increased his stamina.

_I could get used to this_, Marui thought as he licked the final bit of icing off his fork. Sighing contently, he made his way upstairs. Suddenly, he stopped and realized that he didn't know where Marui Bunta slept. He tried looking at every room, but all the rooms looked like a place where Marui Bunta would sleep. Quickly, Marui entered a random room and opened his books to start his homework.

On second thought….

Marui put all his homework, smirking when he realized that the real Marui would probably get in trouble for that. Well, as it wasn't Niou Masaharu who would be blamed, he didn't particularly care.

"Bunta-nii! Why are you in our room?"

Marui quickly looked up to find two similar-looking boys standing at the doorway. "Well… it was closer, and I was tired…" he said, using a sophistry to give reason to his actions.

"But, your room is the closest to the stairs!" one protested. The other one nodded furiously. "But if you're already here, let's play!"

* * *

_I refuse to believe that Bunta goes through this everyday and actually enjoys it_, Marui thought grimly while pretending to wince in pain when one of Marui Bunta's brothers fake-stabbed him with a needle. "Great! Are you feeling okay?" he said with an innocent questioning glance adorning his face.

"Yes Doctor, I'm fine." Marui said sarcastically. At first he was worried that he would lose his disguise, but the Marui twins didn't even seem to notice that his character had changed. He sighed as the younger twin wrapped his arm with bandages, even though he hadn't even made a scratch on the tennis player's skin.

Finally, the twins handed him a lollipop and pushed him into Marui Bunta's bed, bringing the blankets up before Marui could even protest. Not that Marui intended to stop them anyway; he was exhausted, and thankful to be able to escape the two doctor-imitating kids. Marui sighed and waited for the twins to close his door and exit the room. Suddenly, he remembered something and grinned.

Marui slowly and silently got out of bed, and turned on the lights before closely inspecting Marui Bunta's room. It seemed normal enough, with a few pictures of the tennis team placed on his headboard, and his uncompleted homework scattered on the desk. Unsatisfied, Marui decided to look closer, and opened every drawer and closet before he noticed something that put an evil glint in his eyes.

"Marui Bunta's Private Diary: Keep out!" it read, with the cover decorated with pastries. Of course, Marui planed to do the opposite of what the diary intended him to do, and instead searched even more to find a key. After 10 fruitless minutes of searching, Marui decided to look where he find the diary, and behold, a tiny silver key sat right next to the book.

Unable to resist the suspense, Marui shoved the key inside and turned it, the lock opening with a rewarding "click". Without hesitating, he started to scan his eyes over every page, wanting to ingest every bit of info that the diary had to offer. It started off jokingly, and Marui even found himself involuntarily smiling at some parts that the pink-head had wrote. But after a while, the entries took a turn for the worse.

His eyes widened at what was written. He stared at the words for what seemed like hours, until he finally closed the book and relocked it, making it appear that it had never been moved in the first place.

Deciding to try to forget what he had read, Marui turned off the lights and slipped back into his bed, forcing his eyes closed and mind blank.

* * *

"RING RING RING, RIIIIIIIING!" the alarm clock shouted for 10 minutes until Marui finally woke up, glaring death at the small device. Looking at the thing properly, he found out that it was only 7:00 a.m. Their morning tennis practice started at 8, after all, and Niou Masaharu had learned to treasure every last second of sleep until he got out of bed 5 minutes before their morning practice started, and casually walked to school with no intent of rushing.

Marui Bunta, on the other hand, made a noticeable attempt to wake up early everyday. Key word: attempt. He often explained that his body was refusing to move, and that his sleepiness wasn't helping either.

Which was probably why exactly 5 minutes after the alarm clock had gone off (and Marui had ignored it), the doorbell rang. His mother, who had awoken much earlier, happily trudged to the door and opened it.

"Good morning- why, aren't you Niou, one of Bunta's tennis friends? Great! Please, come in..." With a welcoming gesture, Marui Bunta's mother lead Niou inside.

"Yeah, 'morning mom- I mean, Marui-san. May I please see Ni- Marui?" Niou said awkwardly, trying to cover up his mistakes. Then he realized that Niou Masaharu wasn't nearly as nice, and gave up trying to imitate the trickster.

"Oh, hey Niou!" Marui said, his words not once fumbling, "Why are you here?"

Niou looked visibly annoyed at the sight of his body being occupied by another soul, but tried to smirk and imitate the trickster. "Just coming to, um, wake you up? Because, Sanada-fukubuchou said that our morning practice is... a few minutes earlier today, so I thought that you wouldn't make it there in time..." he finished uneasily. Luckily, Marui sensed his nervousness, and smiled. "Yeah, I'll be there in a second!" he said, and rushed upstairs to change. A few moments later, he returned, dressed in Rikkai's yellow and black tennis uniform and carrying his tennis bag.

When he walked over to the place that Niou was sitting, Niou dropped his façade and glared at Marui. "You forgot my cake!" he hissed, and pointed to pile of pastries on the table that Marui hadn't noticed before. Sighing, Marui went back over and shoved a few wrapped cakes into his bag, before dragging the unwilling Niou out the door and informing his "mother" that he was leaving.

**A/N Don't worry, I haven't forgotten about Marui's diary. I'll probably explain what it says in a later chapter, and the same with Niou's books. **


End file.
